Technical Field
The present disclosure relates to a heterojunction bipolar transistor, and to a method of forming the same.
Description of the Related Art
For high frequency applications, bipolar transistors, and in particular heterojunction bipolar transistors (HBT), often provide a preferred solution. It is known to integrate heterojunction bipolar transistors with standard complementary metal oxide semiconductor CMOS processes, such that one or more HBTs can be implemented in a CMOS process with relatively few additional photolithography masks.
However, in advanced CMOS technologies, such as 28 nm or beyond, integration of heterojunction bipolar transistors becomes much more challenging due to constraints such as the limitation in the permitted height of the device, which is generally incompatible with known HBT structures, or leads to a complex and costly process.